The captain started right engine with no problems, using 'high residual temperature' procedures. During left engine start, the engine never got above 20 percent ng during the normal engine start procedure and ng rolled back when he released the start switch. There was no light off. I noticed that the engine condition lever was in fuel cutoff. The captain then said that he was going to perform a high residual start. He had control of the condition lever, start switch and ignition switch. As the engine started, there was a loud pop from the left side of the aircraft. The captain put the engine condition lever to fuel cutoff, mentioning that the left engine cowling had 'popped open.' we then did a normal shutdown of the aircraft and deplaned the passenger. In my opinion, the cowl was 'blown' open by an explosive fuel air mixture that entered the cowl by air currents of the tailwind, blowing fuel vapor from the engine tail exhaust extension into the back of the cowling. There was never a high exhaust gas temperature during the start attempt (198 degrees C), nor were there any signs of fire (warning bell or lights). I never saw any smoke blow by the cockpit windows. The design of the engine exhaust extension facilitated fuel vapor collection in the engine nacelle during tailwind conditions if light off is delayed. Supplemental information from acn 220547: initiated a normal left engine start and inadvertently left the condition lever in fuel off position. This process only lasted about 5 seconds with no start up. Then did an interrupt start motoring vent open into a start. When ignition and condition lever were brought up and on, a pop was heard and the left cowling had popped open. The wind at the time of engine start was reported at 220 degrees at 9 KTS. But the winds were switching around and it may have been a left quartering headwind to a left quartering tailwind at the time of engine start up.

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Original NASA ASRS Text

Title: AN LTT CREW SUFFERED A BLOWN OPEN ENG COWLING DURING A FAULTY STARTING PROC.

Narrative: THE CAPT STARTED R ENG WITH NO PROBLEMS, USING 'HIGH RESIDUAL TEMP' PROCS. DURING L ENG START, THE ENG NEVER GOT ABOVE 20 PERCENT NG DURING THE NORMAL ENG START PROC AND NG ROLLED BACK WHEN HE RELEASED THE START SWITCH. THERE WAS NO LIGHT OFF. I NOTICED THAT THE ENG CONDITION LEVER WAS IN FUEL CUTOFF. THE CAPT THEN SAID THAT HE WAS GOING TO PERFORM A HIGH RESIDUAL START. HE HAD CTL OF THE CONDITION LEVER, START SWITCH AND IGNITION SWITCH. AS THE ENG STARTED, THERE WAS A LOUD POP FROM THE L SIDE OF THE ACFT. THE CAPT PUT THE ENG CONDITION LEVER TO FUEL CUTOFF, MENTIONING THAT THE L ENG COWLING HAD 'POPPED OPEN.' WE THEN DID A NORMAL SHUTDOWN OF THE ACFT AND DEPLANED THE PAX. IN MY OPINION, THE COWL WAS 'BLOWN' OPEN BY AN EXPLOSIVE FUEL AIR MIXTURE THAT ENTERED THE COWL BY AIR CURRENTS OF THE TAILWIND, BLOWING FUEL VAPOR FROM THE ENG TAIL EXHAUST EXTENSION INTO THE BACK OF THE COWLING. THERE WAS NEVER A HIGH EXHAUST GAS TEMP DURING THE START ATTEMPT (198 DEGS C), NOR WERE THERE ANY SIGNS OF FIRE (WARNING BELL OR LIGHTS). I NEVER SAW ANY SMOKE BLOW BY THE COCKPIT WINDOWS. THE DESIGN OF THE ENG EXHAUST EXTENSION FACILITATED FUEL VAPOR COLLECTION IN THE ENG NACELLE DURING TAILWIND CONDITIONS IF LIGHT OFF IS DELAYED. SUPPLEMENTAL INFO FROM ACN 220547: INITIATED A NORMAL L ENG START AND INADVERTENTLY LEFT THE CONDITION LEVER IN FUEL OFF POS. THIS PROCESS ONLY LASTED ABOUT 5 SECONDS WITH NO START UP. THEN DID AN INTERRUPT START MOTORING VENT OPEN INTO A START. WHEN IGNITION AND CONDITION LEVER WERE BROUGHT UP AND ON, A POP WAS HEARD AND THE L COWLING HAD POPPED OPEN. THE WIND AT THE TIME OF ENG START WAS RPTED AT 220 DEGS AT 9 KTS. BUT THE WINDS WERE SWITCHING AROUND AND IT MAY HAVE BEEN A L QUARTERING HEADWIND TO A L QUARTERING TAILWIND AT THE TIME OF ENG START UP.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.